Media stocker, paper feeding device, and method of controlling posture of recording media

ABSTRACT

A media stocker includes: a paper feeding table configured to support plural recording media in a stacked state; a lifting and lowering mechanism configured to lift and lower the paper feeding table; a bottom plate attached to the paper feeding table and configured to receive the recording media placed thereon and support the recording media such that a downstream side end in a conveying direction of the recording media on the paper feeding table moves up and down relatively to an upstream side end in the conveying direction; and a control section configured to make an angle of the bottom plate adjustable such that a surface of the recording medium at the top extends along a direction substantially orthogonal to a lifting and lowering direction of the paper feeding table.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from Japanese Patent Application No. 2009-213832 filed on Sep. 15, 2009, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a media stocker, a paper feeding device, and a method of controlling the posture of recording media.

BACKGROUND

A media stocker configured to stock a large number of recording media vertically lifts and lowers a paper feeding table to thereby bring recording media on the paper feeding table into contact with a pickup roller. Therefore, unlike a system for rotating the paper feeding table to press the recording media against the pickup roller described in, for example, JP-A-2005-330027 (document 1), the media stocker can stock an enormous number of recording media exceeding several hundred recording media, for example, four hundred recording media.

On the other hand, in recent years, recording mediums, for example, label sheets embedded with RFID media capable of performing communication by RFID are developed and put to practical use. Among such recording media, there are recording media in which the RFID media are embedded while being shifted from the center portion between an upstream side end and a downstream end in a conveying direction of the recording media.

The thickness of the RFID media is not so large and is, for example, about 0.1 mm. However, when the recording media in which the RFID media are arranged to be shifted are set in the media stocker, the RFID media having such thickness are stacked and the recording media incline to be higher on a side where the RFID media are provided.

On the other hand, in the technical field of the media stocker, it is a technical common sense that the posture of a recording medium at the top to be picked up is most desirably horizontal. This is because, if the recording medium at the top inclines, a conveying direction of recording media conveyed by the pickup roller also inclines following the inclination of the recording medium at the top. Such inclination causes a deficiency in a separating mechanism located on the downstream side in the conveying direction of the pickup roller and configured to separate only the recording medium at the top. This deficiency causes a conveyance failure. As the deficiency in the separating mechanism, for example, the recording medium at the top cannot be correctly separated or, depending on the structure of the separating mechanism, a skew occurs in the recording medium at the top.

The present invention is devised in view of such points and it is an object of the present invention to make it possible to maintain horizontal, even when media having different thicknesses on the upstream side and the downstream side in the conveying direction are stacked and stocked, for example, when the recording media having the RFID media in a position shifted from the center are used, the posture of a recording medium at the top of the stacked recording media.

SUMMARY

According to an aspect of the present invention, there is provided a media stocker including: a paper feeding table configured to support plural recording media in a stacked state; a lifting and lowering mechanism configured to lift and lower the paper feeding table; a bottom plate attached to the paper feeding table and configured to receive the recording media placed thereon and support the recording media such that a downstream side end in a conveying direction of the recording media on the paper feeding table moves up and down relatively to an upstream side end in the conveying direction; and a control section configured to make an angle of the bottom plate adjustable such that a surface of the recording medium at the top extends along a direction substantially orthogonal to a lifting and lowering direction of the paper feeding table.

According to another aspect of the present invention, there is provided a paper feeding device including: a paper feeding table configured to support plural recording media in a stacked state; a lifting and lowering mechanism configured to lift and lower the paper feeding table; a bottom plate attached to the paper feeding table and configured to receive the recording media placed thereon and support the recording media such that a downstream side end in a conveying direction of the recording media on the paper feeding table moves up and down relatively to an upstream side end in the conveying direction; a control section configured to make an angle of the bottom plate adjustable such that a surface of the recording medium at the top extends along a direction substantially orthogonal to a lifting and lowering direction of the paper feeding table; and a pickup roller configured to pick up the recording medium at the top placed on the paper feeding table and convey the recording medium at the top in a predetermined conveying direction.

According to still another aspect of the present invention, there is provided a method of controlling the posture of recording media in a media stocker including: a paper feeding table configured to support plural recording media in a stacked state; a lifting and lowering mechanism configured to lift and lower the paper feeding table; and a bottom plate attached to the paper feeding table and configured to receive the recording media placed thereon and support the recording media such that a downstream side end in a conveying direction of the recording media on the paper feeding table moves up and down relatively to an upstream side end in the conveying direction, the method including adjusting an angle of the bottom plate such that a surface of the recording medium at the top extends along a direction substantially orthogonal to a lifting and lowering direction of the paper feeding table.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall front view of a paper feeding device according to an embodiment of the present invention;

FIG. 2 is a plan view of an example of a recording medium attached with an RFID medium;

FIG. 3 is a side view of a paper feeding table and a lifting and lowering mechanism therefor;

FIG. 4 is a front view of the paper feeding table and the lifting and lowering mechanism therefor;

FIG. 5 is a schematic diagram for explaining the position of a shaft as a swing center of a bottom plate of the paper feeding table;

FIG. 6 is a schematic diagram for explaining a role and optimum restoring force of coil springs included in a control section;

FIG. 7 is a front view of a paper feeding table according to another embodiment of the present invention;

FIG. 8 is a front view of a paper feeding table according to still another embodiment of the present invention; and

FIG. 9 is a perspective view of the paper feeding table.

DETAILED DESCRIPTION

FIG. 1 is an overall front view of a paper feeding device according to an embodiment of the present invention. In a paper feeding device 31 according to this embodiment, a pickup roller 41 and a separating mechanism 51 are attached to a media stocker 101. The paper feeding device 31 stocks, for example, a recording medium 11 shown in FIG. 2 in the media stocker 101.

FIG. 2 is a plan view of an example of the recording medium 11. The recording medium 11 has an RFID medium 12 capable of performing communication by RFID. The RFID medium 12 includes, although not shown in FIG. 2, an IC chip configured to execute the communication by RFID and an antenna connected to the IC chip. In the recording medium 11, the RFID medium 12 is arranged to be shifted to a downstream side end 11D in a conveying direction indicated by an arrow in FIG. 2 from a center portion C between an upstream side end 11U and the downstream side end 11D in the conveying direction. The thickness of the RFID medium 12 in the recording medium 11 attached with the RFID medium is, for example, about 0.1 mm.

As shown in FIG. 1, the paper feeding device 31 picks up and conveys, with the pickup roller 41, the recording medium 11 at the top among recording media 11 stocked in the media stocker 101, separates, with the separating mechanism 51, the recording medium 11 at the top from the other recording media 11, and feeds the recording medium 11 at the top to a paper feeding port (not shown) of an image forming apparatus.

The pickup roller 41 feeds, with pickup conveyance by friction, not only the recording medium 11 at the top but also the recording media 11 located under the recording medium 11 at the top to the separating mechanism 51.

The pickup roller 41 is located near RFID media 12 in the recording media 11 stocked in the media stocker 101 (near a side having larger thickness of the recording media 11 stocked in the media stocker 101). In other words, the pickup roller 41 is located on one end side in the conveying direction of the recording media 11.

The separating mechanism 51 includes a conveying roller 52 and a separating roller 53 opposed to each other via a feeding path SP for the recording media 11. The conveying roller 52 rotates when the pickup roller 41 starts rotation in order to pick up and convey the recording media 11. The conveying roller 52 applies conveying force to the recording media 11 picked up and conveyed by the pickup roller 41. The separating roller 53 rotates following the conveying roller 52 when the conveying roller 52 starts rotation. The separating roller 53 stops the rotation when the recording media 11 picked up and conveyed by the pickup roller 41 reach a position immediately before the separating mechanism 51.

Specifically, the paper feeding device 31 stops the rotation of the separating roller 53 in the position immediately before the recording medium 11 at the top and the recording media 11 located under the recording medium 11 at the top reach the separating mechanism 51. Therefore, the separating mechanism 51 can stop the recording media 11 located under the recording medium 11 at the top by bumping the recording media 11 located under the recording medium 11 at the top against the separating roller 53. In other words, the separating mechanism 51 separates only the recording medium 11 at the top from the other recording media 11. The recording medium 11 at the top separated from the other recording media 11 is conveyed by the conveying roller 52 to the paper feeding port (not shown) of the image forming apparatus.

Only the recording medium 11 at the top separated from the other recording media 11 is conveyed in this way because conveying force applied to the recording medium 11 at the top by the rotation of the conveying roller 52 is stronger than frictional force between the recording medium 11 at the top and the stopped recording medium 11 located right under the recording medium 11 at the top. In this way, the paper feeding device 31 loosens, with the separating mechanism 51, the plural recording media 11 picked up and conveyed by the pickup roller 41 and separates and conveys only the recording medium 11 at the top.

The rotation of the separating roller 53 is stopped by a one-way clutch (not shown). It is determined by using, for example, a sensing value of a sensor (not shown) arranged between the pickup roller 41 and the separating mechanism 51 that the recording media 11 reaches the position immediately before the separating mechanism 51.

The separating mechanism 51 does not always have to be the system explained above and may be, for example, a reverse roller system.

The media stocker 101 is explained below. FIG. 3 is a side view of a paper feeding table 103 and a lifting and lowering mechanism 104 therefor. FIG. 4 is a front view of the paper feeding table 103 and the lifting and lowering mechanism 104 therefor.

In the media stocker 101, the paper feeding table 103 is attached to one base plate 102 of sheet metal to be freely lifted and lowered. The lifting and lowering mechanism 104 allows the paper feeding table 103 to be freely lifted and lowered. Therefore, the lifting and lowering mechanism 104 is explained and then the paper feeding table 103 is explained in detail below.

The lifting and lowering mechanism 104 includes a pair of lifting and lowering rollers 105 attached under the paper feeding table 103 to be rotatable around a horizontal rotation axis and a pair of rear lifting and lowering rollers 106 located on the opposite side of the paper feeding table 103 across the base plate 102. In the lifting and lowering mechanism 104, the rear lifting and lowering rollers 106 are attached to a single roller holding member 107 of sheet metal to be rotatable around a horizontal rotation axis. The lifting and lowering mechanism 104 couples and fixes the paper feeding table 103 and the roller holding member 107 via elongated communication holes 108 of a long hole shape formed in three streaks in the base plate 102 and extending in the vertical direction. Therefore, the lifting and lowering mechanism 104 supports the paper feeding table 103 with the pair of lifting and lowering rollers 105 located on the front side of the base plate 102 and the pair of rear lifting and lowering rollers 106 located on the rear side of the base plate 102 to allow the paper feeding table 103 to be freely lifted and lowered along the base plate 102. From the viewpoint of supporting fulcrums for supporting the paper feeding table 103, sections where the pair of lifting and lowering rollers 105 are set in contact with the base plate 102 are supporting fulcrums located at the bottom and sections where the pair of rear lifting and lowering rollers 106 are set in contact with the base plate 102 are supporting fulcrums located at the top.

The lifting and lowering mechanism 104 includes a pair of belt winding mechanisms 109 located on both sides of the base plate 102. The belt winding mechanisms 109 are mechanisms obtained by laying endless belts 111 over a pair of upper and lower pulleys 110. The pulley 110 located in the lower part rotates with power from a driving source (not shown) to rotate the endless belts 111. Therefore, the lifting and lowering mechanisms 104 couple and fix coupling sections 112 provided in the roller holding member 107 to the respective pair of endless belts 111 to transmit the rotation of the endless belt 111 to the roller holding member 107 and lift and lower the paper feeding table 103.

The paper feeding table 103 is explained in detail below.

The paper feeding table 103 has a bottom plate 113. The bottom plate 113 receives the plural recording media 11 directly placed thereon and supports the recording media 11. The paper feeding table 103 swingably holds the bottom plate 113. Specifically, in the paper feeding table 103, a shaft 114 orthogonal to a pickup and conveying direction of the recording media 11 by the pickup roller 41 is located in a center portion of the bottom plate 113. The bottom plate 113 is attached rotatably around the shaft 114. This makes the bottom plate 113 swingable.

FIG. 5 is a schematic diagram for explaining the position of the shaft 114 as a swing center of the bottom plate 113 of the paper feeding table 103. As shown in FIG. 5, the bottom plate 113 of the paper feeding table 103 includes the shaft 114 attached to the paper feeding table 103 between a pair of coil springs 116 functioning as urging members. The arrangement position of the shaft 114 of the bottom plate 113 is further examined. In this embodiment, in the paper feeding table 103, the shaft 114 is arranged in the center portion of the bottom plate 113. As width in upstream and downstream directions in the conveying direction of the recording media 11, the width of the bottom plate 113 and the width of the recording medium 11 coincide with each other. Therefore, the position of the shaft 114 as the swing center of the bottom plate 113 is located in the center portion C of the recording media 11 (see FIG. 5). What is important in this embodiment is that the shaft 114 of the bottom plate 113 is located in the center portion C in the upstream and downstream directions in the conveying direction of the recording medium 11.

However, the shaft 114 of the bottom plate 113 does not always have to be located in the precise center portion C in the upstream and downstream directions in the conveying direction of the recording media 11. The shaft 114 of the bottom plate 113 only has to be arranged on a vertical surface between the RFID media 12 of the recording media 11 placed on the bottom plate 113 and the upstream side end 11U or the downstream side end 11D in the conveying direction of the recording media 11 in a direction far from the RFID media 12. In FIG. 5, a range in which the shaft 114 of the bottom plate 113 should be arranged is indicated by DR.

Therefore, in the paper feeding table 103, in a state in which the recording media 11 are set such that the RFID media 12 are located further on the downstream side in the conveying direction than the center portion of the recording media 11 (a state in the upper part of FIG. 5), the shaft 114 of the bottom plate 113 only has to be arranged on the vertical surface between the RFID media 12 and the upstream side end 11U in the conveying direction of the recording media 11 in a direction far from the RFID media 12. Conversely, when the recording media 11 are set such that the RFID media 12 is located further on the upstream side in the conveying direction than the center portion of the recording media 11 (a state in the lower part of FIG. 5), the shaft 114 of the bottom plate 113 only has to be arranged on the vertical surface between the RFID media 12 and the downstream side end 11D in the conveying direction of the recording media 11 in a direction far from the RFID media 12.

The paper feeding table 103 includes a control section 115 configured to control a rotation angle of the bottom plate 113 such that the surface of the recording medium 11 at the top extends along a direction orthogonal to the lifting and lowering direction of the paper feeding table 103, more specifically, to bring an inclination angle of the recording medium 11 at the top, which inclines according to the thickness of the RFID media 12, with respect to the horizontal surface closer to zero degree. The control section 115 has the pair of coil springs 116 as urging members. The coil springs 116 are compression coil springs configured to accumulate urging force in a compressed state, arranged on both the upstream and downstream sides of the recording media 11 placed on the bottom plate 113 across the shaft 114, and urge the bottom plate 113 upward. The coil springs 116 have the same number of turns and the same urging force. The coil springs 116 are separated from the shaft 114 by the same distance. Therefore, the bottom plate 113 is maintained horizontal in a vacant state in which no recording medium 11 is placed on the bottom plate 113.

In such a configuration, the media stocker 101 stocks and stores a large volume of recording media 11 and prepares for pickup and conveyance by the pickup roller 41. To stock the recording media 11, the media stocker 101 places the recording media 11 on the bottom plate 113 of the paper feeding table 103. In this way, a process for stacking the plural recording media 11, in which the RFID media 12 are provided to be shifted from the center portion between the upstream side end and the downstream side end in the conveying direction, and holding the recording media 11 with the paper feeding table 103, which is freely lifted and lowered, is performed.

FIG. 6 is a schematic diagram for explaining a role and optimum urging force of the coil springs 116 included in the control section 115. It is assumed that, in the paper feeding table 103, the recording media 11 are set such that the RFID media 12 are located further on the downstream side in the conveying direction than the center portion C of the recording media 11.

The thickness of the recording media 11 is different across the center portion thereof on a side on which the RFID media 12 are provided and a side on which the RFID media 12 are not provided. Therefore, as the number of stacked recording media 11 increases, the recording media 11 inclines to be higher on the side on which the RFID media 12 are provided (see FIG. 6A).

On the other hand, the weight of the recording media 11 is different by the weight of the RFID media 12 across the center portion thereof on the side on which the RFID media 12 are provided and the side on which the RFID media 12 are not provided. As the recording media 11 as a whole, this weight difference increases in proportion to an increase in the number of stacked recording media 11. Therefore, the media stocker 101 according to this embodiment maintains the posture of the recording medium 11 at the top horizontal making use of such a weight difference that occurs between the upstream side and the downstream side in the conveying direction across the center portion C of the recording media 11. Specifically, in an example shown in FIG. 6, since the RFID media 12 are located further on the downstream side in the conveying direction than the center portion C of the recording media 11, the weight on the downstream side in the conveying direction is larger than the weight on the upstream side in the conveying direction. Therefore, the coil spring 116 arranged on the downstream side in the conveying direction is compressed and the coil spring 116 arranged on the upstream side in the conveying direction is stretched. The bottom plate 113 inclines to fall to the downstream side in the conveying direction. As a result, the posture of the recording medium 11 at the top is maintained horizontal.

However, whether the posture of the recording medium 11 at the top is maintained horizontal depends on a value of a sum of the restoring force of the compressed coil spring 116 and the restoring force of the stretched coil spring 116. If such restoring forces of the coil springs 116 are set to optimum restoring forces, it is possible to maintain the posture of the recording medium 11 at the top horizontal. On the other hand, if the restoring forces of the coil springs 116 are too strong, as shown in FIG. 6C, the inclined state of the recording media 11 is not completely eliminated and the recording medium 11 at the top still keeps the inclined state. If the restoring forces of the coil springs 116 are too weak, as shown in FIG. 6D, the recording media 11 incline in the opposite direction and the recording medium 11 at the top also inclines in the opposite direction.

Therefore, in selecting the coil springs 116, first, a difference between the thickness on the side on which the RFID media 12 are provided and the thickness on the side on which the RFID media 12 are not provided and a difference between the weight on the side on which the RFID media 12 are provided and the weight on the side on which the RFID media 12 are not provided are measured in the recording media 11. Then, the coil springs 116 having a spring rate at which a compression amount of the pair of coils springs 116 obtained when load equivalent to the measured weight is applied is equal to the measured thickness dimension only has to be selected. Further, to maintain the posture of the recording medium 11 at the top horizontal irrespectively of the number of stacked recording media 11 on the bottom plate 113 of the paper feeding table 103, it is desirable to use the coil springs 116 having a progressive rate at which the load and the compression amount linearly change.

In addition, as in this embodiment, the shaft 114 of the bottom plate 113 is located in the center portion C in the upstream and downstream directions in the conveying direction of the recording media 11. Then, even if the recording media 11 are set such that the RFID media 12 are located further on the downstream side in the conveying direction than the center portion C of the recording media 11 in the paper feeding table 103, it is possible to maintain the posture of the recording medium 11 at the top horizontal under the same condition. Conversely, even if the recording media 11 are set such that the RFID media 12 are located further on the upstream side in the conveying direction than the center portion C of the recording media 11 in the paper feeding table 103, it is possible to maintain the posture of the recording medium 11 at the top horizontal under the same condition.

In this way, a process for controlling an angle of the bottom plate 113 configured to receive the recording media 11 placed thereon and support the recording media 11 in the paper feeding table 103 to bring an inclination angle of the recording medium 11 at the top, which inclines because of the thickness of the RFID media 12, with respect to the horizontal surface closer to zero degree is performed.

As explained above, according to this embodiment, as a result of maintaining the posture of the recording medium 11 at the top horizontal, the direction of pickup and conveyance of the recording media 11 by the pickup roller 41 is also maintained horizontal. Thereafter, it is possible to correctly perform separation and feeding in the separating mechanism 51. This makes it possible to prevent a conveyance failure of the recording media 11.

Another embodiment of the present invention is explained with reference to FIG. 7. Components same as those explained with reference to FIGS. 1 to 6 are denoted by the same reference numerals and signs and explanation of the components is omitted.

FIG. 7 is a front view of the paper feeding table 103 according to this embodiment. The paper feeding table 103 according to this embodiment is applied to the media stocker 101 of a system for setting the recording media 11 such that the RFID media 12 are located further on the downstream side in the conveying direction than the center portion C of the recording media 11 in the paper feeding table 103.

In the media stocker 101 shown in FIG. 1 and the like, the bottom plate 113 is swingably provided in the paper feeding table 103. On the other hand, in the media stocker 101 according to this embodiment, the shaft 114 of the bottom plate 113 is located on the distal end side of the paper feeding table 103 and the bottom plate 113 is provided rotatably around the shaft 114. In the media stocker 101 according to this embodiment, the control section 115 is located in a position where the control section 115 urges the bottom plate 113 upward further on the downstream side in the conveying direction of the recording media 11 than the vertical surface passing the shaft 114 of the bottom plate 113.

In such a configuration, when the recording media 11 are stacked on the bottom plate 113 of the paper feeding table 103, the coil springs 116 are compressed by the weight of the RFID media 12 of the recording media 11. Therefore, the recording media 11 are prevented from inclining to be higher on the downstream side in the conveying direction because of the thickness of the RFID media 12. As a result, it is possible to maintain the posture of the recording medium 11 at the top horizontal.

Concerning the media stocker 101 of a system for setting the recording media 11 such that the RFID media 12 are located further on the upstream side in the conveying direction than the center portion C of the recording media 11, the paper feeding table 103 can be applied by interchanging the positions of the shaft 114 of the bottom plate 113 and the coil springs 116 in the upstream and downstream directions in the conveying direction of the recording media 11.

The shaft 114 of the bottom plate 113 only has to be arranged on a vertical surface between the RFID media 12 of the recording media 11 placed on the bottom plate 113 and the upstream side end or the downstream side end in the conveying direction of the recording media 11 in a direction far from the RFID media 12.

A still another embodiment of the present invention is explained with reference to FIGS. 8 and 9. Components same as those explained with reference to FIGS. 1 to 6 are denoted by the same reference numerals and signs and explanation of the components is omitted.

FIG. 8 is a front view of the paper feeding table 103 according to this embodiment. FIG. 9 is a perspective view of the paper feeding table 103. As in the embodiment explained with reference to FIG. 7, the paper feeding table 103 according to this embodiment is applied to the media stocker 101 of the system for setting the recording media 11 such that the RFID media 12 are located further on the downstream side in the conveying direction than the center portion C of the recording media 11 in the paper feeding table 103.

In the media stocker 101 according to this embodiment, a deflecting member 121 is provided in the paper feeding table 103 instead of the bottom plate 113 and the coil springs 116. The deflecting member 121 is an elastic member formed to be bent in a U shape, a piece on the lower side of which is fixed to the paper feeding table 103 and a piece on the upper side of which is the bottom plate 113 configured to receive the recording media 11 placed thereon and support the recording media 11. In the deflecting member 121, a deflecting free end FE side of the bottom plate 113 is arranged on a side on which stacking thickness is increased by the RFID media 12 in the recording media 11 placed on the bottom plate 113. Therefore, in the case of this embodiment, the free end FE of the bottom plate 113 is arranged on the downstream side in the conveying direction of the recording media 11.

In such a configuration, when the recording media 11 are stacked on the bottom plate 113 of the paper feeding table 103, the deflecting member 121 is compressed by the weight of the RFID media 12. Therefore, the recording media 11 are prevented from inclining to be higher on the downstream side in the conveying direction because of the thickness of the RFID media 12. As a result, it is possible to maintain the posture of the recording medium 11 at the top horizontal.

Concerning the media stocker 101 of the system for setting the recording media 11 such that the RFID media 12 are located further on the upstream side in the conveying direction than the center portion C of the recording media 11, the paper feeding table 103 can be applied by reversing the direction of the deflecting member 121 in the upstream and downstream directions in the conveying direction of the recording media 11.

The control section 115 may control a swinging angle of the bottom plate 113 according to driving of an actuator (not shown). Specifically, the actuator is controlled to be driven to maintain the posture of the recording medium 11 at the top horizontal, whereby the swinging angle of the bottom plate 113 is controlled.

In this embodiment, as the recording media 11 stocked by the media stocker 101, the recording media 11 in which the RFID media 12 are provided to be shifted from the center portion between the upstream side end and the downstream side end in the conveying direction are explained. On the other hand, the recording media 11 do not always have to have the RFID media 12. The operational effects of the media stocker 101 according to this embodiment are realized as long as the recording media 11 have different thicknesses on the upstream side and the downstream side across the center portion in the conveying direction and have larger weight on the side on which the thickness is larger.

In addition, in this embodiment, the structure in which the bottom plate 113 rotates around the fixed shaft 114 is explained. On the other hand, the bottom plate 113 does not always need the physical shaft 114 in the rotation center thereof. Specifically, the bottom plate 113 may swing around an imaginary shaft. Moreover, the shaft in this case does not always have to be fixed. As an example, the shaft may be an imaginary shaft, the position of which shifts according to the swing of the bottom plate 113.

Further effects and modifications can be easily derived by those skilled in the art. Therefore, a wider aspect of the present invention is not limited by the specific details and the representative embodiment represented and described above. Therefore, various modifications are possible without departing from the spirit or the scope of the general concept of the invention defined by the appended claims and their equivalents. 

What is claimed is:
 1. A media stocker comprising: a paper feeding table configured to support plural recording media in a stacked state; a lifting and lowering mechanism configured to lift and lower the paper feeding table; a bottom plate attached to the paper feeding table and configured to receive the recording media placed thereon and support the recording media such that a downstream side end in a conveying direction of the recording media on the paper feeding table moves up and down relatively to an upstream side end in the conveying direction; and a control section configured to make an angle of the bottom plate adjustable such that a surface of the recording medium at a top extends along a direction substantially orthogonal to a lifting and lowering direction of the paper feeding table.
 2. The media stocker according to claim 1, wherein the control section includes a pair of urging members configured to elastically support the bottom plate on the upstream side and the downstream side in the conveying direction of the recording media across substantially a center portion of the bottom plate.
 3. The media stocker according to claim 2, wherein the bottom plate includes a shaft attached to the paper feeding table between the pair of urging members, and the control section includes urging members configured to respectively urge the bottom plate upward on both the upstream side and the downstream side in the conveying direction of the recording media across the shaft.
 4. The media stocker according to claim 3, wherein the shaft of the bottom plate is arranged in a vertical surface passing substantially a center portion in upstream and downstream directions in the conveying direction of the recording media placed on the bottom plate.
 5. The media stocker according to claim 1, wherein the control section is a deflecting member formed by an elastic member formed to be bent in a U shape, a piece on a lower side of which is fixed to the paper feeding table and a piece on an upper side of which is the bottom plate configured to receive the recording media placed thereon and support the recording media.
 6. A paper feeding device comprising: a paper feeding table configured to support plural recording media in a stacked state; a lifting and lowering mechanism configured to lift and lower the paper feeding table; a bottom plate attached to the paper feeding table and configured to receive the recording media placed thereon and support the recording media such that a downstream side end in a conveying direction of the recording media on the paper feeding table moves up and down relatively to an upstream side end in the conveying direction; a control section configured to make an angle of the bottom plate adjustable such that a surface of the recording medium at a top extends along a direction substantially orthogonal to a lifting and lowering direction of the paper feeding table; and a pickup roller configured to pick up the recording medium at the top placed on the paper feeding table and convey the recording medium at the top in a predetermined conveying direction.
 7. The paper feeding device according to claim 6, further comprising a separating mechanism configured to separate only the recording medium at the top from the recording media picked up and conveyed by the pickup roller.
 8. The paper feeding device according to claim 6, wherein the pickup roller is located on one end side in the conveying direction of the recording media.
 9. A method of controlling a posture of recording media in a media stocker including: a paper feeding table configured to support plural recording media in a stacked state; a lifting and lowering mechanism configured to lift and lower the paper feeding table; and a bottom plate attached to the paper feeding table and configured to receive the recording media placed thereon and support the recording media such that a downstream side end in a conveying direction of the recording media on the paper feeding table moves up and down relatively to an upstream side end in the conveying direction, the method comprising adjusting an angle of the bottom plate such that a surface of the recording medium at a top extends along a direction substantially orthogonal to a lifting and lowering direction of the paper feeding table. 